Vitamin A is essential for vision, reproductive function, growth, and the control of cellular differentiation. The long term goal of the proposed research is to investigate the relationship between the metabolism of vitamin A and its derivatives (the retinoids) and the mechanism of action whereby these substances regulate spermatogenesis. The immediate goal of the proposed experiments is to examine the metabolism of retinol in cultured Sertoli cells in detail and to correlate information on this metabolic process with the known action of retinoids on Sertoli cells. Specific Aim 1: Retinoid metabolites formed from 3H-retinol will be extracted and quantitated by HPLC from cultured rat Sertoli cells. Specific Aim 2: The precursor to product relationship within the retinoid metabolites generated by cultured Sertoli cells will be established. Specific Aim 3: The subcellular distribution of retinol and retinoid metabolites in cultured Sertoli cells will be determined. Specific Aim 4: The delivery factors such as plasma retinol binding protein (RBP) which may affect the uptake, metabolism and activity of reinol and retinoic acid in cultured Sertoli cells will be examined. Specific Aim 5: The structures of the major retinoid derivatives or metabolites will be examined and confirmed by mass spectroscopy. Specific Aim 6: Retinol metabolism will be examined in short-term cultures of germinal cells.